U.S. patent number 10,486,273 [Application Number 15/510,036] was granted by the patent office on 2019-11-26 for spindle for a ball screw and method for producing same.
This patent grant is currently assigned to SCHAEFFLER TECHNOLOGIES AG & CO. KG. The grantee listed for this patent is Schaeffler Technologies AG & Co. KG. Invention is credited to Matthias Dohr, Daniel Faber, Fritz Kammerer, Benjamin Wubbolt-Gorbatenko.
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United States Patent |
10,486,273 |
Faber , et al. |
November 26, 2019 |
Spindle for a ball screw and method for producing same
Abstract
The invention relates to a method for producing a spindle for a
ball screw, including the following steps: --introducing, at least
in sections, a thread profile into a flat material section,
--shaping the material section to a hollow cylindrical case, two
lateral edges of the hollow cylindrical case abutting each other
and the thread profile being oriented radially outwards,
--connecting the two lateral edges of the hollow cylindrical case,
and --forming, at least in sections, a supporting structure on a
radially inner face of the hollow cylindrical case to finish the
spindle. A spindle for a ball screw in hybrid design can thus be
manufactured in a simple manner. The spindle can be produced
cost-effectively and yet has high wear resistance and excellent
mechanical load-bearing capacity as well as light weight. The
invention further relates to a spindle manufactured according to
the invention, for use in a ball screw.
Inventors: |
Faber; Daniel (Burgthann,
DE), Wubbolt-Gorbatenko; Benjamin (Herzogenaurach,
DE), Dohr; Matthias (Herzogenaurach, DE),
Kammerer; Fritz (Neuhof-Zenn, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Schaeffler Technologies AG & Co. KG |
Herzogenaurach |
N/A |
DE |
|
|
Assignee: |
SCHAEFFLER TECHNOLOGIES AG &
CO. KG (Herzogenaurach, DE)
|
Family
ID: |
54326243 |
Appl.
No.: |
15/510,036 |
Filed: |
September 3, 2015 |
PCT
Filed: |
September 03, 2015 |
PCT No.: |
PCT/DE2015/200450 |
371(c)(1),(2),(4) Date: |
March 09, 2017 |
PCT
Pub. No.: |
WO2016/041555 |
PCT
Pub. Date: |
March 24, 2016 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20180126500 A1 |
May 10, 2018 |
|
Foreign Application Priority Data
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|
|
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Sep 15, 2014 [DE] |
|
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10 2014 218 405 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23P
15/003 (20130101); F16H 25/2204 (20130101); F16H
25/24 (20130101); B21D 53/24 (20130101); B21D
53/10 (20130101); F16H 2025/2481 (20130101); B21D
5/12 (20130101); B21D 13/04 (20130101) |
Current International
Class: |
F16H
25/24 (20060101); B21D 13/04 (20060101); B21D
53/10 (20060101); B21D 5/12 (20060101); B23P
15/00 (20060101); B21D 53/24 (20060101); F16H
25/22 (20060101) |
Field of
Search: |
;72/67,80,88 ;137/315.4
;409/234 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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101248300 |
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Aug 2008 |
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CN |
|
2446332 |
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Sep 2011 |
|
CN |
|
4131486 |
|
Mar 1993 |
|
DE |
|
10028968 |
|
Dec 2001 |
|
DE |
|
102011081966 |
|
Mar 2013 |
|
DE |
|
102011081966 |
|
Mar 2013 |
|
DE |
|
1914447 |
|
Apr 2008 |
|
EP |
|
2004346987 |
|
Dec 2004 |
|
JP |
|
Primary Examiner: Salone; Bayan
Attorney, Agent or Firm: Volpe and Koenig, P.C.
Claims
The invention claimed is:
1. A method for producing a spindle for a ball screw, the method
comprising: forming a thread profile in a flat material section at
least in some areas, shaping the flat material section into a
hollow cylindrical sleeve, wherein two longitudinal edges of the
hollow cylindrical sleeve abut each other and the thread profile is
directed radially outward, connecting the two longitudinal edges of
the hollow cylindrical sleeve at each of two axial end sections of
the hollow cylindrical sleeve and spaced away from the thread
profile, and forming a support structure on a radial inner side of
the hollow cylindrical sleeve at least in some areas.
2. The method according to claim 1, wherein the flat material
section is a sheet metal section with a small material thickness
that is separated from a web of sheet metal semifinished
product.
3. The method according to claim 1, wherein the thread profile is
formed as a round thread with at least one thread turn for holding
spherical roller bodies of a ball screw.
4. The method according to claim 1, wherein the connection of the
two longitudinal edges of the hollow cylindrical sleeve is realized
by joining at least in one section by creation of a longitudinal
seam.
5. The method according to claim 4, wherein the longitudinal seam
is subjected to a surface treatment, including at least one
grinding, polishing, or honing.
6. A method for producing a spindle for a ball screw, the method
comprising: forming a thread profile in a flat material section at
least in some areas, shaping the flat material section into a
hollow cylindrical sleeve, wherein two longitudinal edges of the
hollow cylindrical sleeve abut each other and the thread profile is
directed radially outward, connecting the two longitudinal edges of
the hollow cylindrical sleeve, and forming a support structure on a
radial inner side of the hollow cylindrical sleeve at least in some
areas, wherein the connection of the two longitudinal edges of the
hollow cylindrical sleeve is realized by pressing a ring onto each
of two axial end sections of the hollow cylindrical sleeve.
7. The method according to claim 6, wherein the hollow cylindrical
sleeve is produced such that the axial end sections have a
non-profiled construction.
8. The method according to claim 1, further comprising constructing
the support structure by injection molding with a plastic
material.
9. The method according to claim 8, wherein the support structure
has a circular ring-shaped cross-sectional geometry that is formed
concentric to the hollow cylindrical sleeve.
10. A spindle for a ball screw produced according to claim 1,
wherein the spindle includes the hollow cylindrical sleeve with the
radially outer thread profile and the support structure formed on a
radial inner side of the hollow cylindrical sleeve.
11. The method according to claim 6, wherein the flat material
section is a sheet metal section with a small material thickness
that is separated from a web of sheet metal semifinished
product.
12. The method according to claim 6, wherein the thread profile is
formed as a round thread with at least one thread turn for holding
spherical roller bodies of a ball screw.
13. The method according to claim 6, wherein the connection of the
two longitudinal edges of the hollow cylindrical sleeve is realized
by joining at least in one section by creation of a longitudinal
seam.
14. The method according to claim 13, wherein the longitudinal seam
is subjected to a surface treatment, including at least one
grinding, polishing, or honing.
15. The method according to claim 6, further comprising
constructing the support structure by injection molding with a
plastic material.
16. The method according to claim 15, wherein the support structure
has a circular ring-shaped cross-sectional geometry that is formed
concentric to the hollow cylindrical sleeve.
17. A spindle for a ball screw produced according to claim 6,
wherein the spindle includes the hollow cylindrical sleeve with the
radially outer thread profile and the support structure formed on a
radial inner side of the hollow cylindrical sleeve.
18. The method according to claim 1, wherein a connection between
the two longitudinal edges of the hollow cylindrical sleeve is
formed without a weld seam.
Description
BACKGROUND
The invention relates to a spindle for a ball screw and a method
for producing this spindle.
For example, ball screws are widely used in automotive technology,
primarily as actuators, because they enable a low-loss conversion
of a rotational motion into a linear motion and vice versa. Such a
ball screw comprises essentially a spindle and a nut or sleeve
surrounding this spindle coaxially, between which ball-shaped
roller bodies are arranged. Producing these components that are
required for a ball screw from a solid material by means of cutting
methods is challenging and therefore cost-intensive.
From the prior art, different methods and constructions of ball
screws are known that permit relatively simple and therefore
economical production of these ball screws. From DE 100 28 968 A1,
such a sleeve is known for a screw drive that is formed from a
sheet-metal blank that is flat at the beginning and in which a
threaded profile is formed on one side and that is ultimately bent
into a longitudinally slotted, hollow cylindrical sleeve, such that
the threaded profile forms an internal thread on the sleeve. Roller
bodies of the screw drive roll on the internal thread of the sleeve
and an external thread on a threaded spindle, wherein a rotational
motion is converted into a translational motion. During the
production process of the sleeve, however, a longitudinal slot is
produced in the sleeve, which can be completely closed only by
pressing the sleeve into a hole provided with a corresponding fit.
One disadvantage is that the rolling bodies of the screw drive
cannot roll without reactions in the area of this longitudinal
slot.
From DE 10 2011 081 966 A1, a method for producing a threaded part
as a composite part, a roller screw drive, a linear actuator, and
an electromechanical brake booster with such a composite part are
known. The threaded part is formed as a composite part consisting
of a thread turn and a tubular support part, wherein the thread
turn is produced by a shaping process.
The tubular support part is preferably produced by a molding
process, for example, injection molding or die casting, and
simultaneously connected during this process with the thread turn
using a material-bonding or positive-locking fit. Preferably, the
support part is produced by die casting from a metal or injection
molding from a plastic. According to one embodiment presented in
that document, the threaded part is formed by a spiral-shaped or
helical, wound sheet-metal strip with a flat, rectangular cross
section, wherein a flat, channel-like recess is pressed in the
sheet-metal strip as a thread turn. The windings of the sheet-metal
strip are connected to each other, for example, by spot welding, by
axial welding seams, or by a helical welding seam along the
abutting longitudinal edges of the sheet-metal strip to form the
threaded part that is then connected to the plastic support part by
an injection molding process. This is disadvantageous in that,
among other things, at least one weld seam to be realized with high
accuracy is required to be created that also has a large
longitudinal extent.
SUMMARY
The invention is based on the objective of providing a simplified
method for producing a spindle for a ball screw. A spindle for a
ball screw is also to be provided that functions without an
additional, radially outer enclosing structure.
The invention starts from the knowledge that the production of
hollow cylindrical sheet-metal shaped parts can be simplified by
rolling a flat material blank, which minimizes, among other things,
a seam length of the edges of the rolled material blanks to be
connected.
The invention will first describe a method for producing a spindle
for a ball screw. The objective mentioned above is achieved by a
method that has the following steps: Forming a thread profile in a
flat material section in at least some areas, Shaping the material
section into a hollow cylindrical sleeve, wherein two longitudinal
edges of the hollow cylindrical sleeve abut each other and the
threaded profile is directed radially outward, Connecting the two
longitudinal edges of the hollow cylindrical sleeve, and Forming a
support structure on the radial inner side of the hollow
cylindrical sleeve at least in some areas for completing the
spindle.
By the use of this method, a spindle with an external thread for a
ball screw can be produced very economically. By connecting the
hollow cylindrical sleeve along its two straight longitudinal edges
abutting each other after the shaping process, a required
connection seam length is significantly reduced in comparison to a
sheet-metal strip would, for example, helically into a tube and
connected along the edge sides. In addition, the method according
to the invention is especially suitable for continuous production.
Furthermore, the method enables the production of spindles with
different diameters and/or thread profiles in a very advantageous
way.
According to one refinement of this method it is provided that the
material section is a sheet-metal section with low material
thickness. Through the use of metallic sheets for the material
section, a high mechanical load capacity and durability of the
spindle produced according to the method can be achieved.
Preferably, the sheet metal section is cut from a web-shaped
sheet-metal semifinished product. In this way, among other things,
a continuous production process is possible for producing spindles
formed according to the invention. The threaded profile can be
formed either before the cutting of the material section
continuously from an endless web-shaped semifinished product or
after the cutting of the material section into the separated
material sections.
According to another favorable construction of the method, it is
provided that the thread profile is formed as a round thread with
at least one thread turn for holding ball-shaped roller bodies of a
ball screw. In this way, the ball-shaped roller bodies typically
used in ball screws are guided without a problem in the thread
profile and roll in this profile.
In another refinement of the method, it is provided that the
connection of the two longitudinal edges of the hollow cylindrical
sleeve is realized by joining in at least some sections while
creating a longitudinal seam. This produces a reliable mechanical
connection of the longitudinal edges of the hollow cylindrical
sleeve that abut each other after the molding process, wherein the
longitudinal edges abut each other with no gaps and reliably
prevent expansion of the hollow cylindrical sleeve of the spindle
over its entire longitudinal extent.
According to another continuation of the method, the longitudinal
seam is subjected to a surface treatment, for example, grinding,
polishing, or honing. This realizes smooth running of a ball screw
equipped with the spindle produced according to the method, because
the roller bodies of the ball screw can also roll over the
longitudinal seam with practically no reaction.
According to another embodiment, the connection of the two
longitudinal edges of the hollow cylindrical sleeve of the spindle
is realized by pressing a ring on each of the two axial end
sections of the hollow cylindrical sleeve. This eliminates the
otherwise necessary weld seam to be formed in at least some
sections for joining the longitudinal edges of the hollow
cylindrical sleeve that abut each other after the shaping process.
The weld seam eliminated in this method alternative leads to
significant simplifications in terms of processing, because weld
seams are technically difficult to produce on thin sheet-metal
parts and many times can be produced only in the course of a
complicated laser welding process. In addition, a hardening process
of the hollow cylindrical sleeve necessary under some circumstances
no longer must be realized after connecting the longitudinal edges,
because the hardening can no longer be negatively affected by a
thermal joining process. Geometrical changes occurring due to the
hardening process can also be compensated more easily and
deformation due to the thermal joining is avoided.
According to another advantageous construction of the method, the
axial end sections of the hollow cylindrical sleeve has a
non-profiled construction. This produces a particularly more
secure, ideally full-area seating of each ring on one of the two
axial end sections of the hollow cylindrical sleeve. Alternatively,
the rings can also be shrunk, e.g., thermally onto the profile-free
axial end sections of the hollow cylindrical sleeve.
Another favorable construction of the method provides that the
support structure is formed, from a plastic material, in
particular, during the injection molding. The plastic introduced
into the hollow cylindrical sleeve preferably during the injection
molding process produces a mechanically close-fitting connection,
in particular, a material-bonding and positive-locking connection
between the radially inner support structure and the hollow
cylindrical sleeve coaxially surrounding the inner support
structure with its outer thread profile. Here, the support
structure primarily increases the bending stiffness of the final
spindle, while the hollow cylindrical sleeve formed from the metal
sheet primarily absorbs the point loads caused by the ball-shaped
roller bodies rolling in the thread profile and distributes these
loads over a larger area before they are introduced into the
support structure. Due to hybrid construction produced in this way,
a relatively high mechanical load capacity and wear resistance of
the spindle produced according to the invention is achieved in
connection with a low weight and simultaneously low production
costs. Alternatively, the support structure can also be formed from
a metallic material, for example, a sintered metal, a metal foam,
or a metal injected into the hollow cylindrical sleeve.
According to another refinement, the support structure has a
circular ring-shaped cross-sectional geometry that is formed in the
production method concentric to the hollow cylindrical sleeve. Due
to the preferably tubular construction of the support structure in
the interior of the hollow cylindrical sleeve, a high mechanical
stiffness of the spindle formed in this way is produced, as well as
a significantly reduced weight in comparison to a completely filled
hollow cylindrical sleeve.
The subject matter of the invention is also a spindle for a ball
screw. Here it is provided that the spindle has a hollow
cylindrical sleeve with a radially outside thread profile and that
a support structure is formed on the radial inside of the hollow
cylindrical sleeve. This makes a simple, continuous, and
cost-optimized production of the spindle possible, which provides
excellent wear resistance with relatively low weight, and thus is
suitable for use in automotive technology.
BRIEF DESCRIPTION OF THE DRAWINGS
For better understanding of the invention, a drawing accompanies
the description. Components with identical construction have the
same reference symbols. Shown in the drawing are:
FIGS. 1 to 6 an illustration of the sequence of a first method
variant for producing a first embodiment of a spindle for a ball
screw according to the invention, and
FIGS. 7 to 9 a simplified illustration of a second method variant
for producing a second embodiment of a spindle for a ball screw
according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 to 6 show, accordingly, the illustration of the sequence of
the first method variant for producing a first embodiment of a
spindle for a ball screw. A flat, rectangular material section 10
is cut from a not-shown, endless web-shaped semifinished product
during a first processing step. The material section 10 shown in
cross section in FIG. 1 is preferably a rectangular sheet metal
section 10 with low material thickness. In the next processing
step, as shown in the cross-sectional illustration of FIG. 2, a
thread profile 12 is formed in the material section 10. The thread
profile 12 is preferably produced as a round thread 14 in which not
shown ball-shaped roller bodies of a similarly not-shown ball screw
can roll with low friction. The formation of the thread profile 12
can be realized by any method known from the prior art, for
example, thread pressing. Deviating from the method sequence
explained above, it is also possible to form the thread profile 12
continuously in the web-shaped semifinished product and then to cut
the material section.
The thread profile 12 is here formed so that after rolling the
initially flat material section 10, at least one continuous thread
turn 16 is produced for holding the roller bodies. The thread
profile 12 extends as shown in the top view according to FIG. 3 on
the material section 10 up to parallel longitudinal edges 18, 20 or
to narrow sides of the material section 10, while both axial end
sections 22, 24 have profile-free constructions. The axial end
sections 22, 24 are reflection symmetrical relative to each other
and each have approximately the shape of a right triangle.
As shown in FIG. 4, in a subsequent processing step, the profiled
material section 10 is shaped with the help of a suitable shaping
process into a hollow cylindrical sleeve 30, wherein the thread
profile 12 is arranged radially outward with respect to a
longitudinal center axis 32 of the hollow cylindrical sleeve 30.
The two longitudinal edges 18, 20 of the material section 10 are
formed by this shaping process ideally to realize a completely
abutting contact. In addition, the axial end sections 22, 24
without thread profile after the completion of the shaping process
can be seen in FIG. 4.
In a subsequent processing step, as shown in FIG. 5, a hollow
cylindrical ring 34, 36 is pressed onto an axial end section 22,
24. Through the two rings 34, 36, the longitudinal edges 18, 20 are
connected mechanically rigidly to each other at least in the area
of the axial end sections 22, 24. In this way, the creation of a
technically demanding weld seam or solder seam is not required for
joining the two longitudinal edges 18, 20. Before or after the
pressing of the two rings 34, 36, the hollow cylindrical sleeve 30
can be subjected to a hardening process with its radially outer
thread profile 12. An inner diameter of the rings 34, 36 is to be
dimensioned with respect to the outer diameter of the axial end
sections 22, 24 of the hollow cylindrical sleeve 30 so that an at
least slight press-fit connection is realized between these parts.
A width b of the axial end sections 22, 24 without profile is
preferably equal to or greater than a width h of the rings 34,
36.
As FIG. 6 shows, the hollow cylindrical sleeve 30 is provided
radially on the inside with a support structure 42, wherein a
spindle 40 for a ball screw with the features of the invention is
created. For the sake of better clarity in the drawing, the two
rings 34, 36 are not shown in FIG. 6.
The support structure 42 is here formed, as an example, concentric
to the hollow cylindrical sleeve 30 and to the longitudinal center
axis 32. It is formed, for example, from a fiber-reinforced plastic
that further increases the mechanical load capacity of the spindle
40. By use of the support structure 42, a spindle 40 is created in
a hybrid construction in which the metallic sleeve 30 receives and
simultaneously distributes, with its thread profile 12, the surface
pressures through the point contact with ball-shaped roller bodies,
while the support structure 42 provides the necessary stiffness for
the spindle 40. Just the plastic of the support structure 42 would
not be sufficient to continuously receive the surface pressures of
the rolling balls. Thus, a mechanically high load capacity and
consequently expensive sheet metal or metallic material is required
only for the hollow cylindrical sleeve 30 with the thread profile
12 formed in this sleeve, while the support structure can be formed
from a relatively economical plastic as a filler material.
The formation of the support structure 42 can be realized, for
example, by injection molding, wherein a not-shown cylindrical core
of an injection molding tool is introduced axially into the hollow
cylindrical sleeve 30 and also the hollow cylindrical cavity
between the core and the sleeve 30 is filled for creating the
support structure 42 with the material of the support structure 12.
Injecting the plastic produces a mechanically especially
close-fitting, thus positive-locking and material-bonding
connection between the shaped support structure 42 and a corrugated
inner surface 44 of the hollow cylindrical sleeve 30 as a negative
image of the thread profile 12. Therefore, in addition to the two
rings 34, 36, an additional connection between the abutting
longitudinal edges 18, 20 of the hollow cylindrical sleeve 30 is
created, so that easy and smooth running of the ball screw equipped
with the spindle 40 is achieved.
Deviating from the embodiment of spindle 40 shown in FIG. 6, the
inner space 46 of the hollow cylindrical sleeve 30 can also be
completely filled with plastic if the weight of the spindle is of
lower significance.
FIGS. 7 to 9 show in a simplified illustration a second method
variant for producing a second embodiment of a spindle for a ball
screw. In an initially flat material section 50, in a first
processing step, a thread profile 52 is formed, in turn, which is
preferably constructed as a round thread 54 for ball-shaped roller
bodies and has at least one thread turn 56 for guiding the rolling
roller bodies.
The thread profile 52 extends between two parallel longitudinal
edges 58, 60 of the material section 50. In contrast to the first
method variant according to FIGS. 1 to 6, the thread profile 52
extends, however, into the area of the two axial end sections 62,
64. With respect to the other construction of the material section
50, in order to avoid repetition, refer to the explanations with
regard to FIGS. 1 to 3.
As can be seen from the perspective view of FIG. 8, the initially
flat material section 50 is shaped by the use of a suitable shaping
process, in turn, into a hollow cylindrical sleeve 70, wherein the
thread profile 52 is arranged radially outward with the helical
surrounding thread turn 56 with respect of a longitudinal center
axis 72 of the sleeve 70 and the two longitudinal edges 58, 60 of
the material section 50 abut each other over their entire
surface.
As another difference to the first method variant, the two
longitudinal edges 58, 60 are mechanically rigidly joined in
another, preferably thermal processing step, for example, by laser
welding or soldering, continuously under the creation of a
longitudinal seam 74. Alternatively, the connection of the two
longitudinal edges 58, 60 can also be realized by adhesive bonding,
swaging, pressing, or the like. After the connection of the two
longitudinal edges 58, 60 by preferably thermal joining, a surface
treatment of the longitudinal seam 74 by grinding, polishing, or
honing can be performed, in order to further optimize the running
behavior of the ball screw. The hollow cylindrical sleeve 70 with
the thread profile 52 formed in this sleeve is preferably subjected
to a hardness treatment, in order to increase its wear
resistance.
As the longitudinal section according to FIG. 9 shows, in a final
processing step, the completion of the second embodiment of a
spindle 80 for a ball screw is realized, in turn, by forming a
support structure 82 that is preferably formed from an optional,
additional fiber-reinforced plastic. With respect to further
structural details of the support structure 82 and its production,
refer to the statements in the scope of the description of FIG.
6.
In contrast to the first method variant, in the case of the second
method variant, it is possible with preferably welded longitudinal
seams to produce the spindle 80 as one continuous section of nearly
arbitrary length. For this purpose, the thread profile 52 is formed
initially continuously in the endless web-shaped, initially flat
semifinished product, from this the hollow cylindrical sleeve 70 is
formed continuously by a shaping process, and finally its
longitudinal edges 58, 60 are welded to each other continuously at
least in some sections. In parallel, the plastic for forming the
support structure 82 is fed continuously into the already welded
hollow cylindrical sleeve 70 by an injection welding tool. Finally,
a section completed in this way can be cut to length into spindles
80 with a nearly arbitrary length.
REFERENCE NUMBERS
10 Flat material section 12 Threaded profile, external thread 14
Round thread 16 Thread turn 18 Longitudinal edge of the material
section 10 20 Longitudinal edge of the material section 10 22 Axial
end section of the material section 10 24 Axial end section of the
material section 10 30 Hollow cylindrical sleeve 32 Longitudinal
center axis of the sleeve 30 34 First ring 36 Second ring 40
Spindle 42 Support structure 44 Inner surface of the support
structure 46 Inner space 50 Flat material section 52 Threaded
profile, external thread 54 Round thread 56 Thread turn 58
Longitudinal edge of the material section 50 60 Longitudinal edge
of the material section 50 62 Axial end section of the material
section 50 64 Axial end section of the material section 50 70
Hollow cylindrical sleeve 72 Longitudinal center axis of the sleeve
70 74 Longitudinal seam 80 Spindle 82 Support structure h Width of
the rings 34, 36 b Width of the profile-free end sections 22,
24
* * * * *